Why Thanksgiving will not be on Chanukah again

This year (5774) is the 17th year of the 19 year cycle. Since the leap month is not until Adar, Chanukah will be "early" in the solar year. The 19 year cycle will cause any particular Hebrew date to fall on the same secular date every 19 years. It can differ by one day based on the Solar leap year adding in February 29 every four years. This will also be affected by the fact that the secular leap year will be dropped in 2100. The first day of Chanukah (25 Kislev) appeared as followed in the current (303) cycle, using the 0 based count

year          cycle         date of 25 Kislev

5757             0            Fri.      6 Dec.

5758             1            Wed. 24 Dec.

5759             2            Mon. 14 Dec.

5760             3            Sat.    4 Dec.

5761             4            Fri.    22 Dec.

5762             5            Mon. 10 Dec.

5763             6            Sat.  30 Nov.  Thanksgiving was Thurs. Nov. 28

5764             7            Sat.  20 Dec.

5765             8            Wed.  8 Dec.

5766             9            Mon. 26 Dec.

5767            10           Sat.   16 Dec.

5768            11           Wed.   5 Dec.

5769            12           Mon.  22 Dec.

5770            13           Sat.   12 Dec.

5771            14           Thu     2 Dec.

5772            15           Wed. 21 Dec.

5773            16           Sun.    9 Dec.

5774            17           Thu.   28 Nov.     *THANKSGIVING*

5775            18           Wed.  17 Dec.

5776             0            Mon.    7 Dec.

Thus we see that in cycle years 6 and 17, the first day of Chanukah will be within a week of Thanksgiving as part of the regular cycle depending on when the fourth Thursday of November occurs. Note the way the cycle of year 17 continues. Thus in months with 5 Thursdays, (it would be 29 or 30 November), Thanksgiving is the week before (November 22 or 23).

5793 - Sun. 28 Nov

5812 - Wed. 29 Nov. - 2051 Thanksgiving is on November 23

5831 - Fri.    28 Nov. - 2070 the day after Thanksgiving

5850 - Mon.  28 Nov. - 2089

5869 - Thu.   29 Nov. - 2108 Thanksgiving is on November 22

5888 - Sun.  30 Nov. - 2127 Thanksgiving is November 28.

5907 - Mon. 28 Nov. - 2146 Thanksgiving is November 24
5926 - Fri.   29 Nov. - 2165 Thanksgiving is November 28
5945 - Mon. 29 Nov. 2184
5964 -  Thu. 1 Dec. 2203 Here is the next change because of the century adjustment
5983 - Sat. 30 November 2222 Thanksgiving is November 28.

As a result of the fact that 2100 is not a leap year, Thanksgiving can no longer match up with Chanukah. Since Passover must be in the spring, the calendar will skip a leap year once the Mashiach comes and the Sanhedrin reinstated. This will move the dates back so they will not keep getting later and "wrap around" as does the Moslem calendar. We cannot calculate the dates using the current fixed calendar past that time.

As of 1910, Pesach was on April 24. One month earlier, March 24, after the equinox, was Taanis Esther (13 Adar II). If the Sanhedrin had been re-instituted, that may have been the year that the leap year would have been postponed to the following year. This last occurred in 2005 and will occur again in 2024. If leap year would be postponed, then since Passover would be March 23 (in 2024), the following year would have Passover before the equinox (March 13) which would not be allowed. Thus, that year would be a leap year and Taanis Esther would be on March 13 and Passover would be the following month on April 13. Similarly, Chanukah following the "skipped" leap year would be November 26 instead of December 26, while the Chanukah following the "new" leap year would be approximately 20 days later or December 6. This would reset the 19 year cycle and we would have to recalculate the following years.

Of course for this to occur, the Mashiach would have come and we would no longer be in exile. As a result, Thanksgiving would no longer be immediately relevant.

Note that since 2100 was not a secular leap year, the first day of Chanukah is no longer Nov. 28 or 29 but begins appearing on November 29 or 30. This will also cause the prayer for rain in the Shmoneh Esrei to move from maariv December 4 or 5 (which started in 1900) to December 5 or 6. The change did not occur as we ended the last century because 2000 was a leap year since it is divisible by 400.

That is why 25 Kislev kept appearing on 28 November in the 1800's but on 27 November in the 1700's.